The device relates to a skin movement detector which detects displacements on a skin surface using a pressure-sensitive element having a diaphragm.
Skin movement detectors detect the soundness of muscles governed by a nerve by causing a skin surface corresponding to the muscles to be moved by, e.g., electrically stimulating the nerve.
A conventional skin movement detector is shown in FIGS. 5 and 6. A pressure-sensitive element 52 is disposed at the inner bottom of a cylindrical case 51 which has an opening. A membrane 53 made of a soft material is attached to the case so as to cover the opening of the case 51 and contact a skin surface. At the periphery of the membrane 53 is a flange-like portion 54 extending outwardly from the case. On an inner surface of the membrane 54 is a projection 55 whose tip is formed integrally with the membrane and contacts the pressure-sensitive element 52.
According to this skin movement detector, the flange-like portion 54 is displaced by movement of the skin causing its base in contact with the case 51 to serve as a fulcrum. The displacement is transmitted to the projection 55 to change the biasing force applied from the projection to the pressure-sensitive element 52, thereby allowing skin movements to be detected.
In the above construction, the movement of the membrane 53 and thus the projection 55 is limited because a portion of at which the membrane is adhesively fixed to the case 51. As a result, the sensitivity of the membrane is undesireably impaired, particularly, in directions other than in the direction shown by arrow D in FIG. 5. Further, if projection 55 is moved too far in the direction shown by arrow D, the pressure-sensitive element 52 may be damaged.